Radio frequency amplifier



" Sept. 16,` 1941.

J. L. HATHAWAY ET AL RADIO FREQUENCY AMPLIFIER Filed March 50, 1958 2 Sheets-Sheet l INVEN T R5 JA RRETT L. HATHA WAY ATTORNEY.

OUTPUT C'. RES/DES ".J. 1 HATHAWAY ET A1. 2,255,882

RADIO FREQUENCY AMPLIFIER Sept. 16, 1941.

2 sheets-sheet 2 Filed March 50, 1938 .SRSQ

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N A Y B Patented Sept. 16, 1941 RADIO FREQUENCY AMPLIFIER Jarrett L. Hathaway,Manhasset, and Wilbur C. Besides, Jackson Heights, N. Y., assignors to Radio Corporation of America, a corporation of Delaware Application March 30, 1938, Serial No. 198,838

7 Claims. (Cl. 179-171) This invention relates to radio frequency ampliiiers and, more particularly, to improved coupling circuits for said amplifiers.

An object of the present invention is to efficiently couple together a plurality of stages of radio frequency amplification. Another object is to provide a source of well-regulated radio frequency without resorting to resistance loading ofv the source.

Still another object is to provide a radio frequency amplifier having a high effective grid to cathode impedance in its operating condition.

Briefly, our invention involves a radio frequency amplifier in which the output energy is derived from a tuned cathode circuit instead of from a tuned plate circuit, as heretofore known and used. The neutralization which is necessary, just as with plate coupled amplifiers, is provided for by means of either a split grid circuit or a split cathode circuit. The amplifier constructed according to our invention may be conveniently modulated by supplying one or more of the electrodes with a modulated direct current instead of pure direct current. Any of the circuits of our invention; may be conveniently used for frequency multiplication. For such operation the cathode circuit is tuned to the multiple frequency desired.

Referring, now, for a more complete disclosure of our invention, to the subsequent detailed description which is accompanied by drawings in which Figure 1 illustrates an embodiment of our invention, lwhile Figures 2, 3, 4, 5 and 6 illustrate modifications thereof and Figure 7 illustrates the application of our invention to push-pull operation.

In, Figure'l reference numeral I indicates a radio frequency amplifying tube having a grid 2, a plate 3 and a cathode 4. The input circuit 6 which is coupled to grid 2 by means of condenser 'I comprises coil 8 and tuning condenser 9. The grid circuit of the tube is completed by means of radio frequency choke I I and resistance I2 to ground. The output circuit which is coupled to cathode 4 comprises coil I3, which is tuned by condenser I4 to the desired frequency. Plate potential EE applied to plate 4 may be either pure direct current or it may be modulated in any known manner. As an example, there is shown in Figure 7 one way in which the direct current supply may be modulated. The manner of modulating the current is described more fully with reference to Figure 7. In order to neutralize the amplifier the grid coil 8 is of the coil is` connected to the cathode circuit through neutralizing condenser NC.

Figure 2 is similar to Figure 1 except that insteadof using the split grid neutralization a tap on the cathode coil, I6 is grounded and the end of the coil remote-from the cathode is connected to the grid 2 through neutralizing condenser NC. Otherwise, the circuit is similar to Figure 1.

In Figure 3 our invention has been applied to a radio frequency amplifier using a tetrode tube instead of a triode. As shown in the figure screen grid 5 is energized from a source of potential Es through radio frequency choke I5. The amplifier shown in this ligure acts as a modulator for either the plate voltage supply Ea. or the screen grid voltage supply Es, or both may be a modulated source of direct current. This has been indicated in the drawings by labeling the potential sources Ea and Es as modulated or constant potential. Neutralization is provided in the same way as in Figure 1, though cathode :neutralization may be employed.

Figure 4 is similar to Figure 1, `except that a beam power tube is shown with the screen connected to the plate and thus operated as a triode. The tetrode connection shown in Figure 3 may also be employed with this tube.

The modification shown in Figure 5 employs an amplifier tube having a shield by-passed to ground between the grid and cathode to reduce capacity coupling. The use of such a tube obvilates the necessity of neutralization. This modification is otherwise similar to that shown in Figure 1.

Figure 6 shows the application of our invention to an amplifier using a pentode tube. A split condenser across the cathode coil is used to Vestablish a ground as shown in this circuit. Any of the other neutralizing systems described may be used. y

In Figure 7 the application of our invention to `push-pull operation of radio frequency amplifiers is shown. The amplifier is energized from source 1 coupled to the input circuit 6. Inl this figure thel amplifier may be modulated by means of modulator transformer I8 connected in the anode supply circuit El, as shown, in the left hand side of the ligure or, alternatively, it may be modulated by means of a transformer connected in the lead to power supply E-l-z forming a part of the cathode circuit, as shown in the right hand side of the figure. The modulating frequencies are applied to terminals X, X or tapped and the tap grounded. The lower end Y, Y, or both, as desired. At the right of this Y iigure E- and E|4 denote opposite polarities v tube may be made to operate in cathode cou.-

pledcircuits at about percent efliciency at 40 megacycles. ments show that the cathode tank or output impedance is in the'order of 275 ohms.

Comparative measurements of. the' output voltage 4between a cathode coupled and a plate coupled amplifier indicateV that the voltage developed across' the tank circuit of the cathode Under these conditions, measures control grid andra cathode, an input circuitrcomthermionic discharge tube having an anode, a control grid and a cathode, an input circuit comprising a tapped inductance and a condenser connected across said inductance, one end of saidA inductance being connected to said grid and said tap grounded, a low impedance output circuit Yconnected between lsaid cathode Vand ground and a connection including a neutralizing condenser connected between the end ofsaid inductance ref mote from said grid connection and saidcathode. 4. A radio frequency amplifier comprising a thermionic discharge tube having an anode, a

prisi-ng a tapped inductance and a condenserconcoupled circuit is approximately 11/2 times the voltage developed across the tank of a plate coupled Y amplifier .when it was resistance Yloaded to give an equivalent output impedance. Was vfurther noted that .an increase in power inthe amplifier grid tank circuit occurs when the plate 'voltage'isjapplied to `the amplifier.v It is notedV that this applicationU of plate fvo1t` agecauses a marked decrease of. amplifier rec-v tified-grid current. This is because thefgrid to` cathode Vimpedance is very low without plate voltage but when theplate voltage is applied impedance lrises-due to the degenerative eflectsof i, the cathode-coupling;`

While we--have particularly shown and described several' forms ofour invention vit is-tov be understood Vthat thel invention is not .lim-

ited to` theforms illustrated but -modications' may be made'within Vthe scope of the invention. y Y Y We claim: A

1. 1A radifgfrequenc'y amplifier comprising a thermionic discharge'tube having ari/anode, a

control grid anda cathode, an input circuit 'for said tube comprising akt-uned circuit andV a low impedance output circuit comprising a tuned circuit connectedin series between said cathode andggrid,` means for Yconnecting a source of potential `to said anode andthe junction betweeny for connecting a source of signal modulated -potential to said anode and means for neutralizing theeiect rof Ythe grid to cathode capacity of Vsaid dischargeetube including a neutralizing condenser for applying, ay voltage to said cathode Vvequal and i V opposite phase to that on said grid.

.3. vA radiQV frequency amplifier comprising la amplifier comprising 'a3 Y nected across said inductance, one endV of said inductance vbeing connected to said grid and said tap grounded, a low impedance output circuit connected betweenV said cathode and ground and a connection including a neutralizing condenser connected between the endV of said inductance V remote from, said grid connection and said cathode and means for connecting'a source of potential to said anode.

`54A .radio frequencyamplifier comprising a thermionic discharge tube having at least an anode, a control grid and a cathode,an input Vcircuit comprising a tapped induetance and a condenser connectedacross said'inductance, one end of said V inductance being connected to saidl grid and said motefrom said grid connection and saidcath- 0de and means fcrconnecting a source of signa modulated potentialto said anode. 1

' 6. A radio frequency amplier comprisingl a thermionic discharge tube lheu/ing an anode, Ya cathode, a control grid and a screenV grid, an input circuit comprising a tapped inductance and a condenser connected across said inductancaone end of said inductance being connected to said control grid and saidtap grounded, an output circuit con-V nected between'said cathode and groundl and a connection including a neutralizing condenser vconnected between the end of said inductance remote from said grid connection and said cathode, and means for connectinga source of signal modulated potential to said anode. g

7. A -radio frequency amplifier comprising a thermionic discharge4 tube having an anode, a cathode, a control grid anda screen grid,v an input circuit comprising a tapped inductance and a condenser connected across said inductance, one end of said inductance being connected tosaid control grid and said tap grounded, an output circuit connected between said cathode andground and a connection includingra neutralizing condenser connected between the end of said inductance remote from said grid connection and said cathode, and means for connecting a source`v of signal modulated potential to said anode and said screen grid and decoupling means between said means and said screen grid.

y.LARRET'L L HATHAWAY.

WILBUR c. REsrDEs. 

